| 摘要 |
PROBLEM TO BE SOLVED: To provide a high toughness hot tool steel to be used as a production material for a die for hot working, wherein even it is used as a large-sized die stock, a long die life is attained by giving high hardness, and further, danger that cracks are generated during the use of a die is reduced by securing high toughness and ductility. SOLUTION: A hot tool steel is made into an ingot under the condition that the average cooling rate from a solidus temperature at the time of solidification to a liquidus temperature is≥0.025°C/s, the ingot is heated to the temperature range of 1,240 to 1,360°C, and the crystallized carbides and carbonitrides are subjected to solution treatment, thus the one in which the density of the carbides and carbonitrides crystallized in the steel together with oxide-based inclusions is (1)≤0.01 piece in the large-sized one having the diameter of the equivalent circle of >50μm, and is (2)≤100 pieces in the small-sized one having the diameter of the equivalent circle of 1 to 50μm per mm<SP>2</SP>of the cross-section in the steel is obtained. COPYRIGHT: (C)2006,JPO&NCIPI
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